get a few links pointing at you from sites with a reasonably high PageRank, you'll usually get crawled quite quickly and see your site begin to appear within a week. Then you have to start working to get a decent position ;-)
My new sites keep dropping in and out of the index. But they stabilise after awhile. I wouldn't worry about it.
just put a link in a busy and high pr site like dp (e.g. your signature link) and you should get crawled within a day or 2... should then appear in the index within a week or so... however, recently, i've read of a more cases when sites don't get indexed by google after months... i experienced it myself with one of my new sites...
Get links from high PR, frequently crawled sites and concentrate on your site's content and your site should be in there pretty quickly.